In recent years, a body area network (BAN) that communicates between a plurality of communication devices mounted on different locations of the human body has been studied. A BAN is expected to be applied to, for example, the health care field. For example, a small communication device that is connected to a biosensor mounted on a certain part of the human body such as the wrist communicates, by radio, with a controller mounted on another location of the human body, such as the trunk, and thereby transmits biological information that is acquired by the biosensor, to a controller. Then, the controller transmits biological information, with identification information of the person on which the controller is mounted or identification information of the controller, to a medical information management system placed in a medical facility, via, for example, a wireless communication channel.
In this way, in a BAN, communication devices are mounted on the human body, so that the antennas included in the communication devices are preferably small, and, in particular, the size in the direction that is perpendicular to the surface of the human body is preferably small. Furthermore, in the BAN, a plurality of communication devices may be mounted on the human body. In this case, respective communication devices use different frequency bands. Consequently, the antennas included in the communication devices to be utilized in the BAN are able to use a plurality of frequency bands.
Patch antennas that are small are able to use a plurality of frequency bands have been proposed (for example, see Published Japanese Translation of the POT International Publication for Patent Application (Kohyo) No. 2003-516011, Japanese Laid-Open Patent Publication No. 11-150415, Japanese Laid-Open Patent Publication No. 2001-60823 and Japanese Laid-Open Patent Publication No. 2003-258540). The patch antennas disclosed in these patent documents include a plurality of stacked planar conductors (patches).